As an alternative energy source to fossil fuel, solar cells capable of converting sun light to electric power have drawn attention. At present, some of solar cells using crystalline silicon substrates and thin film silicon solar cells have started to be used practically. However, the former has a problem of a high production cost of the silicon substrates and the latter has a problem that the production cost is increased since various kinds of gases for semiconductor production and complicated production facilities are required. Therefore, in both solar cells, it has been tried to lower the cost per electric power output by increasing the efficiency of photoelectric conversion; however, the above-mentioned problems still remain while being unsolved.
As a new type solar cell, there has been proposed a wet type solar cell based on photo-induced electron transfer of a metal complex (see Patent Document 1). As shown in FIG. 18, this wet type solar cell is composed by laminating a photoelectric conversion layer 104 which is a metal oxide semiconductor layer adsorbing a dye, a carrier transporting layer (electrolyte solution) 107 and a catalyst layer 105 in a region surrounded by conductive films (electrode) 102, 106 respectively formed on two glass substrates 100, 101 and sealing layers 103, 103 formed therebetween, and has an absorption spectrum in a visible light region (Conventional Technology 1).
When the wet type solar cell is irradiated with light, electrons are generated in the photoelectric conversion layer 104, the generated electrons transfer to another conductive film 105 and the catalyst layer 105 through the conductive film 102 on a light-receiving plane side and an external electric circuit, and the transferred electrons are further conveyed and turn back to the photoelectric conversion layer 104 owing to the ion in the electrolyte of the carrier transporting layer 107. Electric energy is outputted based on such the series of the flow of the electrons.
However, since a basic structure of the dye-sensitized solar cell described in Patent Document 1 is a structure that the electrolytic solution is injected between the opposed glass substrates with the conductive film. Therefore, it is possible to produce a trial solar cell with a small surface area, but it is difficult to apply this solar cell to a solar cell with a large surface area such as 1 m square. That is, if in such a solar cell, the surface area of one photoelectric conversion device is enlarged, the generated current is increased proportional to the area. However, since a voltage drop in the plane direction of the conductive film to be used for the electrode parts is increased, and the internal series resistance of the solar cell is increased. As a result, a fill factor (FF) in a current-voltage characteristic and a short circuit current at the time of the photoelectric conversion are lowered, resulting in a problem of decrease of the photoelectric conversion efficiency. Further, since two glass substrates with a conductive film are used, the module has problems that the production cost in forming a module of a dye-sensitized solar cell is increased and the weight is increased.
In order to solve the problems on an internal series resistance, there has been proposed a dye-sensitized solar cell module having a plurality of photoelectric conversion devices connected in series in Patent Document 2. In the dye-sensitized solar cell module in Patent Document 2, as shown in FIG. 19, a plurality of photoelectric conversion devices are formed between a glass substrate 110 on which a transparent conductive film (electrode) 112 is formed in a comb-like shape by patterning and a glass substrate 111 on which a transparent conductive film (electrode) 116 and a catalyst layer 115 are formed successively in a comb-like shape by patterning, and a connecting conductive layer 118 interposed between a pair of insulating layers 113 is formed between the adjacent photoelectric conversion devices and this connecting conductive layer 118 electrically connects the upper transparent conductive film 116 and the lower transparent conductive film 112. The photoelectric conversion device is formed by laminating a photoelectric conversion layer 114, a carrier transporting layer 117, and the catalyst layer 115 in this order from the lower transparent conductive film 112 side (Conventional Technology 2).
However, in the dye-sensitized solar cell module proposed in Patent Document 2, since a dye-sensitized solar cell is prepared by pouring an electrolytic medium into between the glass substrates, the problems of cost and weight still remain while being unsolved.
In order to solve these problems, dye-sensitized solar cell modules having a structure in which number of glass substrates is reduced to one are proposed in Patent Documents 3 and 4.
The dye-sensitized solar cell module of Patent Document 3, as shown in FIG. 20, has a photoelectrode 1 having a plurality of transparent electrodes 15 formed discretely, and has a structure in which a dye-sensitized photoelectric conversion device, obtained by laminating a semiconductor layer 16, a dye and an electrolyte layer (electrolyte solution) 3, is formed on each transparent electrode 15, and an opposed electrode 2B contacting the adjacent transparent electrode 15 is formed on the electrolyte layer 3 so as to connect with a plurality of photoelectric conversion devices with each other in series, and the periphery of the respective photoelectric conversion devices is sealed with a cell sealing portion 4B made of a resin (Conventional Technology 3). In addition, in FIG. 20, a reference numeral 8 represents a base film.
Further, a dye-sensitized solar cell module in Patent Document 4, as shown in FIG. 21, has a transparent glass substrate 310 having a plurality of transparent conductive films 112 formed discretely, and has a structure in which a dye-sensitized photoelectric conversion device, obtained by laminating a porous titanium oxide layer 314 adsorbing a dye, an intermediate porous insulating layer 318 having electrolyte, and an opposed electrodes 315, is formed on each transparent conductive films 112, and the opposed electrodes 315 contacts the adjacent transparent conductive films 312 in such a way that the respective photoelectric conversion devices are connected in series, and the periphery of the respective photoelectric conversion devices is sealed with an insulating layer 313, and a top cover is laminated on the insulating layer 313 (Conventional Technology 4).
Patent Document 1: Japanese Patent No. 2664194
Patent Document 2: Published Japanese Translation of a PCT application No. 2002-540559
Patent Document 3: Japanese Unexamined Patent Publication No. 2005-285781
Patent Document 4: International Publican WO97/16838 pamphlet